Mine did that pretty frequently as well. I got in the habit of recalibrating the compass every time I turned on the unit although Garmin suggests only doing so when you travel 100+ miles, experience a large temperature change, and every time you change the batteries. Remember to calibrate as per the instructions, away from vehicles, buildings, etc., and with a clear view of the sky. Sometimes if you walk too slowly or stand still, the 60csx seems to get confused when it's switching between the electronic and magnetic compass. Instructions on adjusting the time it takes to switch between electronic and magnetic compass are found on page 49 of your manual.
~moon